Synopsis
After taking over their parents' company, siblings Yuuhi and Yuamu Oudou are now working at the Alien Trouble Consultancy, an agency focused on hunting extraterrestrials. Though they have yet to actually encounter any aliens, Yuuhi is determined to find one, convinced that an alien made off with his precious "Earthdama." While searching for alien life, Yuuhi and Yuamu come across a peculiar area in the forest where many trees have been knocked down, creating a pattern reminiscent of a crop circle. Curious, they press deeper and discover a mysterious spaceship, which they enter. Inside, they unexpectedly meet Yuudias Velgear, an alien from the Velgear Star Cluster. He is searching for knowledge about Rush Duel, a card game popular among elementary school kids, believing it can end the prolonged war devastating his home world. As the siblings agree to teach Yuudias about Rush Duel, they start to suspect that their first contact with an alien might not be a mere coincidence.